The present invention relates to a process for the production of hydrogen or CO--(CO.sub.2)--H.sub.2 mixtures, i.e. CO--H.sub.2 mixtures optionally incorporated CO.sub.2, but mainly carbon monoxide and hydrogen and known as synthesis gases, from methane or a gaseous mixture containing methane such as natural gas or gas combined with oil.
Synthesis gas is conventionally produced from natural gas either by steam reforming at a temperature of approximately 900.degree. C. and under a pressure between 20 and 30 bar, in the presence of a nickel-based catalyst, or by partial oxidation with oxygen at high temperature (&gt;1200.degree. C.) and under pressure (20 to 30 bar) in specific burners.
EP 303 438 describes a process for the partial oxidation of hydrocarbons into hydrogen and carbon oxides. This process uses steam in addition to oxygen and takes place at high temperature, i.e. at between 870 and 1040.degree. C. and under a pressure of 2 to 3 MPa. However, the mixture formed essentially contains hydrogen and carbon dioxide and is carbon monoxide-depleted. Moreover, the CO selectivity decreases when the partial water pressure and/or temperature are lowered.
Recently Green et al (Catalysis Today 13, 417, 1992; GB 2 239 406) have demonstrated that it is possible to catalyse the partial oxidation reaction of methane by means of transition metals such as Ni, Ru, Rh, Pd, Pt and Ir supported on inert oxides. At low temperature, i.e. between 380.degree. and 780.degree. C. and a pressure between 1 and 20 bar, high synthesis gas yields have been obtained in this way. Among the catalysts studied by the above authors Eu.sub.2 Ir.sub.2 O.sub.7 and Pr.sub.2 Ru.sub.2 O.sub.7 formulations lead to the highest activities. However, these activities decrease significantly with low contact times (W. J. M. Vermeiren et coll., Catalysis Today, 13, 442, 1992). Moroever, the mixed oxide structure of the pyrochlore type of these formulations, revealed before the catalytic test, is destroyed during the test so as to lead to metallic particles dispersed on oxide of rare earths which constitute the active site in the conversion reaction of methane (or natural gas) into synthesis gas (Ashcroft et coll., Catalysis Letters 8, 169, 1991).